Frequency controlling means



Oct. 20, 1936. G. L. USSELMAN FREQUENCY CONTROLLING MEANS Filed Oct. 18, 1932 2 Sheets-Sheet 1 INVENTOR- GEORGE L.U ELMAN BY M ATTORNEY- 2 1936- G. 1.. USSELMAN FREQUENCY CONTROLLING MEANS Filed Oct. 18, 1932 2 Sheets-Sheet 2 INVENTOR- GEORGE L. USSELMAN /wa/m ATTORNEY- Patented Oct. 20, 1936 UNITED STATES FREQUENCY CONTROLLING MEANS George L. Usselman, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application October 18, 1932, Serial No. 638,321

7 Claims.

This invention relates to a method of and means for controlling the frequency of oscillations used in signalling.

More in detail, the object of the present invention is to provide means whereby the frequency of oscillations of considerable intensity may be maintained constant or controlled in an improved manner over an indefinite period of time duration by the use of a simple and inexpensive means.

Frequency control devices have been known heretofore. For example, systems have been known in the prior art to use tuned circuits and audio filters to select the operating band of the transmitter. This scheme, however, has false operating points which permit the transmitter to operate on the wrong frequency.

An object of the present invention is to provide an arrangement wherein but a single operating point is attained, which operating point is the true one.

Another object of the present invention is to provide a new and improved frequency control means which is inexpensive and may be readily applied to transmitters now in use or to new installations.

Briefly, the above objects are attained in accordance with the present invention by the use of a source of low power constant frequency energy of comparatively high frequency, and by the use of phase splitting circuits by means of which the constant frequency energy is split up into portions which have a predetermined phase shift, which portions are fed to separate rectifying means which are also energized in phase by energy from the frequency generating means to be controlled so that shifts of the latter will result in phase rotation between the control frequency and the frequency to be controlled, which phase rotations may be intensified and utilized to adjust the frequency of the generator to be controlled.

The novel features of my invention have been pointed out in detail in the claims appended hereto.

The mode of operation and the arrangement of the invention will be best understood by reference to the drawings attached hereto in which:

Figure 1 shows, merely for purposes of illustration, an embodiment of a frequency determining means in accordance with the present invention;

Figure 2 is a diagrammatic showing of the relation between currents in different portions of the arrangement of Figure 1; while,

Figure 3 shows in detail features of the control device of Figure 1.

Referring tothe drawings, and in particular to Figure 1 thereof, A represents the transmitter whose frequency is to be corrected. The frequency generator in this transmitter may be a simple tuned oscillator circuit broadly as described in Hartley, United States Patent No. 1,472,470, or a long line frequency controlled oscillator as described in United States applications 1 No. 363,660, filed May 16, 1929, Patent Number 1,945,545, granted February 6, 1934 and No. 400,489, filed October 18, 1929, Patent Number 1,945,546, granted February 6, 1934. B represents the constant frequency source. This frequency source may include a crystal controlled oscillator or any other means whereby frequency oscillations which are constant in nature, but which may be of small intensity, are developed. Preferably, this unit may consist of a moderately low frequency crystal oscillator stage and the required number of frequency multiplier and amplifier stages to obtain the correct frequency at which the transmitter is to operate. This unit can be, and is, made to hold extremely accurate frequency but, because the parts are small, the cost will be reasonably small. The constant frequency oscillations developed in B are fed by way of coupling and-blocking condensers l and 2 into a tuned tank circuit 3 comprising a variable capacity F and inductance E.

This reference frequency appearing in 3 is divided into three portions, one of which is applied by way of by-passing and blocking condenser J and phase retarding inductance G to the control electrode 5 of thermionic rectifier V1, another portion of which is applied by way of phase advancing element H to the control electrode 1 of thermionic rectifier V2, while the third portion is supplied by way of non-inductive resistance I to the control electrode 9 of rectifier tube V3.

Direct current biasing potential for the control electrodes 5, I, and 9 of tubes V1, V2, and V3 respectively is sup-plied from source 10 and lead I I by way of resistances R, R1 and R2 connected as shown. Heating current for the filaments or cathodes l3, l5 and ll of tubes V, V1 and V2 is supplied from source 10 by way of circuit FL. Any high frequency oscillations passing through resistancesR, R1, and R2 are shunted to the filament circuits by by-pass condensers C, C1, and C2.

G, H, I, R, R1, and R2 are the phase splitting circuits. V1, V2, and V: are the detector tubes, which may be of the triode type or, as shown, of the screen grid electrode type. In the latter case charging potential for the screen grid electrodes is supplied, as shown, from the source H) by way of a lead [2 connected on the one hand with said screen electrodes and on the other hand with a point on the potentiometer resistance P2 as shown.

Any high frequency potentials appearing on the screen grid electrodes of tubes V1, V2, and V3 are shunted to ground by way of by-pass condensers C3, C4, and C5 connected, as indicated, between the screen grid electrodes and the filament heating circuit FL.

The values of phase splitting elements G, H, I, R, R1, and R2 are such that the excitation energy from reference source B reaches the control grids 5, 1, and 9 of tubes V1, V2, and V3 approximately l20 out of phase and from each other, as indicated in Figure 2. The anodes 16, I1, and I8 of tubes V1, V2, and V3 respectively are connected as shown by way of radio frequency choke coils L1, L2, and L2 and the primary windings I9, 20, and 2| of transformers T1, T2, and T2 respectively to a point on potentiometer resistance P2 connected with source I0. The primary windings I9, 20, and 2| of these transformers are star connected as shown. Any radio frequencies resulting from demodulation of the reference energy from B in the tubes V1, V2, and V2 which get through choke inductances L1, L2, and L2 are bypassed to ground by way of by-pass condensers C5, C6, and C7. Audio frequencies are not grounded by C5, C6, and C2. Excitation energy from the transmitter A is supplied in like phase by way of blocking and coupling condensers 22, 23, and 24 to the anode electrodes I6, I! and I8 respectively of tubes V1, V2, and V3. The demodulated energy flowing in the primary windings I9, 20, and 2| is impressed by way of the secondary windings 21, 29, and 3| of transformers T1, T2, and T2 on to the control grids 28, 30, and 32 respectively of thermionic amplifier tubes V4, V5, and V6 respectively. Biasing potential for the control electrodes of tubes V4, V5, and V6 is supplied by connecting the low potential terminals of each of the secondary windings 21, 29, and 3| to a lead 33 connected to a point on the potentiometer resistance P1. The filaments of the tubes V4, V5, and V6 are supplied with energizing current from the source In by way of filament heating circuit FL, as indicated.

The anode electrodes 36, 38, and 40 of tubes V4, V5, and V6 are connected as shown by way of the primary windings of output transformers T4, T5, and T6 to the high potential terminal of source III. The secondary windings 31, 39, and 4| of these transformers T4, T5, and T6 are connected for poly-phase operation, that is, three-phase operation, with the phase rotating (polyphase) relay or motor 42.

The transformers T4, T5, and To have a threephase output so that relay 42, connected therewith and energized thereby, operates on threephase power supply. The direction of rotation of relay 42 depends on the direction of phase rotation of the power supplied by transformers T4, T5, and Te.

If there is no phase rotation of the power supplied by the transformers T1, T2, and T3, and in turn T4, T5, and T6, the relay or motor 42 is not actuated and the motor D remains stationary. On the other hand, if the resultants of the threephase energy on the anodes of tubes V1, V2, and V3 and the in phase energy supplied from the transmitter rotates due to a shift in frequency of the transmitter energy, the phase of the power supplied by the transformers T1, T2, and T3 to the amplifiers V3, V4, and V5 will rotate and the phase of the power supplied to the relay or motor 42 will rotate in one direction or the other, depending upon the direction of the shift in phase of the like phase energy supplied from the transmitter to the anodes of the tubes V1, V2, and V3. When the frequency and phase of the energy supplied from the transmitter A is proper, a balance will be attained, and there will be no phase rotation of the power supplied to the polarized phase rotation relay or motor 42, and also where the phase rotation or frequency of the demodulated energy is so low that the transformers will not function. The relay, and consequently the motor D, will be inactive and remain inactive until there is an appreciable shift in frequency or phase of the transmitted energy, and energy supplied to V1, V2, and V3 from A. This shift in phase will, when applied to the phase shifted components from source B, cause a rotating field, the direction of rotation of which depends on the direction of phase shift. The relay 42 will be actuated and consequently the motor D.

The motor D is connected, as indicated, with a tuning control, as, for example, a shaft S, which may be connected with a reactance or tuning element in the frequency generator included in the transmitter A, or with any other circuit therein which, if tuned, will determine the frequency of the energy transmitted from transmitter A constant.

In order to explain more fully the operation of the invention reference will be made to Figures 1 and 2. In explaining the operation of the invention it will be assumed that the transmitter A is operated at a frequency somewhat greater than the frequency supplied from the reference source B. As indicated above, the values of the phase shifting elements G, H, I, R, R1, R2, etc, are such that the excitation energy from reference source B reaches the control electrodes 5, "l, and 9 of tubes V1, V2 and V3 approximately 120 out of phase with respect to each other, as indicated in Figure 2, where the vectors G, H, and I represent the potentials reaching the grids by way of elements G, H, and I respectively. The excitation voltage from transmitter A is supplied in like phase to the anodes of tubes V1, V2, and V2. This excitation voltage is represented by the vector T in Figure 2.

As long as B is supplying energy to the grids of tubes V1, V2, and V3, the vectors G, H, and I rotate at a constant rate so that the phase angle between them remains fixed. The phase angle difference in the present case has, for purposes of illustration, been selected as 120. The vector T rotates faster than vectors G, H, and I. If, then, we consider that vectors G, H, and I are standing still, vector T will rotate anti-clockwise at a comparatively low rate. This rate would in most cases correspond to an audio frequency. The anode current output of each of the tubes V1, V2, and V3 may be represented by the resultant values R2, R1, and R2 respectively, as indicated in Figure 2. As the vector T rotates the anode currents in tubes V2, V2, and V1 reach their maximum value successively so that the alternating current component in the plate transformers T1, T2, and T3 is equivalent to three phase alternating current, i. e., polyphasc currents of audio frequencies. The choke coils L1, L2, and L3 and condensers C5, C6, and C7 serve to prevent radio frequency voltages from reaching the audio transformers.

- tions.

The primary and secondary'windings of the three transformers T1, T2, and T3 are connected Y or star so that the direct current supplies may be fed in at the neutral points of the connec- The plate supply is fed in through the primary neutral point. The tubes V1, V2, and V3 are shown here as the screen grid type. Three element tubes may be used by making proper circuit arrangements. When screen grid tubes are used for V1, V2, and V3, the plate voltage should be set at a low value where the plate current changes rapidly with changes of plate voltage, otherwise the plate excitation voltage would not be effective in producing changes in plate current.

The secondary windings 21, 29, and 3| of'the three transformers T1, T2, and T3 are connected to the grids of amplifier tubes V4, V5, V6. The bias for these grids is fed in by lead 33 at the neutral point of the secondary windings, which are also star connected. The output of transformers T1, T2, and T3 isthree phase, polyphase voltage of audio frequency. This voltage is amplified and passed through transformers T4, T5, and T6, the primary and secondary windings of which are also star connected. The plate current for amplifier tubes V4, V5, and V6 is also fed in at the neutral point of the primary winding connections by lead 34 from source It).

The three phase output of transformers T4, T5, and T6 passes into the polyphase phase-rotation relay or motor 42, which, for reasons set forth hereinbefore, is sensitive to the direction of phase rotation of the power supplied to it. The phase rotating relay may be similar to a polyphase watthour-meter, or it may take the novel form shown in Figure 3 of the drawings.

In this particular arrangement the secondary windings 31, 39, and 4| are connected, as shown, to the three phase delta connected field winding 50 of a three phase motor 42. The rotor winding 5| of this motor is on a shaft S1, which drives a contact making and breaking disk 52 having a contact 53 which cooperates with two movable contacts in an obvious manner to complete a circuit through either field winding F1 or F2 of the motor D. Power to energize these windings F1 or F2 when the circuit is closed by 53 may be supplied from a separate source or, as shown, from the source used in the frequency comparing circuits shown in detail in Figure l and included in the rectangle of Figure 3 at the left of the transformers T4, T5, and T6 by way of leads 54 The armature winding of motor D is connected in series with the field winding energizing circuit in the same direction at all times so that when 53 closes a contact the motor D, and consequently the shaft S, rotates in one direction or the other to correct the tune of the circuits in A.

In any case, the relay or motor 42 should be capable of operating on small power supply and at comparatively high frequencies. Moreover, in all cases, the relay or motor 42 should be equipped with proper contacts for operating the reversible motor D so that the motor D has its direction of rotation controlled by the direction of phase rotation of the detector power output.

The motor D, through the shaft S, operates the transmitter tuning or frequency changing apparatus in any known manner. If this frequency change is made to take place in the right direction, the whole circuit will operate to keep the transmitter frequency within a few cycles of the frequency developed in the constant frequency source B. In other words, if the transmitter frequency driftsabove or belowthe frequency of the oscillation developed in B, the polyphase phase-rotation detector will function to correct the transmitter frequency by bringing it back to approximately the same frequency as that of the monitor B.

The specific embodiment of my invention, as shown in Figure 1, may be modified in a number of Ways. For example, artificial lines of different electrical lengths, as disclosed in my United States application, Serial No. 607,932, filed April 28, 1932, may be used to secure the required phase displacement between grids of the detector tubes V1, V2, and V3.

Having thus described my invention and the operation thereof, what I claim is:

1. In an arrangement to be used with a transmitter having a frequency determining element connected therewith, a source of constant frequency oscillations, phase splitting and rectifying circuits, said phase splitting and rectifying circuits including a plurality of tubes having their control grid electrodes energized by out-of-phase currents from one of said sources and their anodes energized by in-phase currents from the other of said sources, a phase rotation motor having its field winding coupled to the anodes of said tubes and its armature winding connected with a contact closing element, a motor having an armature connected with said tuning element, and an energizing circuit therefor including contacts cooperating with said contact closing element.

2. An arrangement as recited in claim 1 in which said phase splitting and rectifying circuits include three tubes having their control grids energized by currents shifted degrees in phase.

3. In a control system to be used with a transmitter having a frequency determining element connected therewith, a source of constant frequency oscillations, phase splitting and rectifying circuits connected with. said source, said phase splitting and rectifying circuits including a plurality of tubes having their control electrodes energized by out-of-phase currents from said source of constant frequency oscillations and their anodes energized by in-phase currents from said transmitter, a phase rotation motor having its field winding connected with the anodes of said tubes and its armature winding connected with a contact closing element, a motor having an armature connected with said tuning element, and an energizing circuit therefor including contacts cooperating with said contact closing means.

4. Means for maintaining the frequency of the oscillations transmitted by a transmitter constant which transmitter has a tuning reactance connected therewith to determine the frequency transmitted including, a source of oscillations of constant frequency, a plurality of thermionic rectifier tubes each having an anode, a cathode and a control electrode, a tank circuit connected with said source, phase shifting means of different character connecting the control electrode of each of said rectifier tubes to said tank circuit whereby energy of like frequency but of different phase angle is applied to the control electrodes of each of said rectifier tubes, an output circuit connected with the anode of each of said rectifier tubes, circuits connecting said transmitter to each of said output circuits to apply oscillations in phase from said transmitter to each of said output circuits, a motor having its armature connected with said tuning reactance, a circuit connected with the field winding of said motor, said circuit including energizing means and contacts, a phase rotation relay comprising a field winding connected through transformer means to the output circuits of said thermionic rectifier tubes, there being a winding in said field for each of said rectifier tubes, the rotor Winding of said phase rotation relay being connected with contact closing means cooperating with the contacts in said motor energizing circuit.

5. Means for maintaining the frequency of the oscillations transmitted by a transmitter constant which transmitter has a tuning reactance connected therewith to determine the frequency transmitted including, a source of oscillations of constant frequency, three thermionic rectifier tubes each having an anode, a cathode and a control electrode, a tank circuit connected with said source, phase shifting means of different character connecting the control electrode of each of said rectifier tubes to said tank circuit whereby energy of like frequency but of phase angles differing by degrees is applied to the control electrodes of each of said rectifier tubes, an output circuit connected with the anode of each of said rectifier tubes, a circuit connecting said transmitter to each of said output circuits to apply oscillations in phase from said transmitter to each of said output circuits, a motor having its armature connected with said tuning reactance, said motor including two field windings wound in opposition, a circuit for energizing said field windings, said circuit including energizing means and normally open contacts, a phase rotation relay comprising a field winding connected through transformer means to the output circuits of said thermionic rectifier tubes, there being a phase winding in said field for each of said rectifiers, the rotor winding of said phase rotation relay being connected with contact closing means cooperating with the contacts in said motor field winding energizing circuit.

6, Means for maintaining the frequency of the oscillations transmitted by said transmitter constant, which transmitter has a tuning reactance connected therewith to determine the frequency transmitted including, a source of high frequency oscillations, a plurality of thermionic rectifier tubes, each having an anode, a cathode and a control electrode, a tank circuit connected with said source, phase shifting means of different character connecting the control electrode of each of said rectifier tubes to said tank circuit whereby energy of like frequency but different phase angle is applied to the control electrodes of said rectifier tubes, an output circuit connected with the anode of each of said rectifier tubes, means for applying oscillations in phase from said transmitter to each of said output circuits, a motor connected with said tuning means, operating means connected with said motor, said operating means being adapted to drive said motor in a direction dependent upon the nature of the current flowing in said output circuits, and coupling means between said operating means and said output circuit.

7. Means for controlling the frequency of a source of oscillations including frequency determining means, by comparing the frequency of said source of oscillations to be controlled with the frequency of a source of constant frequency oscillations comprising a tuned tank circuit including an inductance, reactances coupling points on said inductance to said source of constant frequency oscillations, a plurality of tubes each having an anode, a cathode and a control grid, reactances of different character connecting points on said tank circuit to the control grid of each of said tubes, impedances connected between the control grid and cathode of each of said tubes, circuits of like character connecting said source of oscillations to be controlled to the anode of each of said tubes, a transformer for each of said tubes, a circuit connecting the primary winding of each transformer between the anode and cathode of a corresponding tube, and a control circuit connected on the one hand to the secondary winding of each of said transformers and on the other hand to said frequency determining means.

GEORGE L. USSELMAN. 

